(a) Field of the Invention
This invention relates to cylindrical vibration absorbers mainly used as an engine mount or a suspension bush, and particularly relates to the technical filed of structures of cylindrical vibration absorbers with a dynamic dumper.
(b) Description of the Related Art
As an example of vibration absorbers of this kind, a vibration absorber is known which is formed by connecting inner and outer cylinders through an elastic element and in which a stopper mechanism for restricting relative axial movement of the inner and outer cylinders is provided at least at one axial end of the vibration absorber and a stopper rubber is placed for cushioning the shock caused by the action of the stopper mechanism. Such a vibration absorber is disclosed, for example, in Japanese Unexamined Utility-Model Publication No. S62-16841, Japanese Unexamined Utility-Model Publication No. H02-14855 and Japanese Patent No. 2773004.
In applications of vibration absorbers of this kind to engine mounts, a technique is known that restrains resonance vibrations by attaching a separate dynamic damper to the vibration absorber, resulting in reduced gear noise and booming noise and reduced transmission of idling vibrations. Such a technique is disclosed, for example, in Japanese Unexamined Patent Publication No. H06-241278.
The dynamic damper disclosed in the above document is formed by attaching a damper mass (damper weight) to a metal plate through a rubber, wherein the metal plate is fixed, by bolts or rivets, to a bracket that is fitted on the outer cylinder of the vibration absorber. Therefore, the entire dynamic damper extends radially outward from the outer periphery of the cylindrical vibration absorber. This not only invites a problem that the dynamic damper takes up space, but also takes a lot of trouble for assembly leading to cost rise of the vibration absorber.
On the other hand, as disclosed in Japanese Unexamined Utility-Model Publication No. H04-4541, a structure is proposed in which a dynamic damper is formed by disposing an elastic member at one axial end only of a cylindrical vibration absorber to connect to any one of the inner cylinder, the outer cylinder and the elastic element and attaching a damper weight to the elastic member.